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July 17, 1962
. G. MAURY
ETAL
SEPARATION OF SOLVATED FIXED NITROGEN
FROM COMPOUNDS CONTAINING SAME
Filed May 29, 1958
3,044,853
2 Sheets-Sheet 1
LEAN DONOR
SOLVENT
lac
ll
\
i
I
i
Z
'7
‘
RESIDUAL
-
GAS
,
33
b,
it!‘
I
'9
~\\
,I8a
J 0
2|
T
LIQUID
TREATING
DONOR SOLVENT
,2
/32
34
REcYcLE
AND/OR 3
AQUEOUS
I6
35
1
I
WATER
AQUEOUS HNO
ZONE -L—*—>
3|
NITRATE
\\\\>
25
20
$5912“
OIL
D||_UENT
DONOR
SOLVENT
26
Iy‘
?mgm
R
/30
°“
—->
I
I0
I
u;- AIR
I
28
24
123 0
ELECTRON DONOR
22a
SOLVENT CONTAINING
NITROGEN OXIDES
AND / OR NI TROUS
ACID FROM ANY
SOURCE.
LUCIEN e. MAURY,
WATER
GEORGE
29
FIG.1
F. NAHILL.
INVENTORS
BY
AGENT.
July 17, 1962
L‘ G. MAURY ETAL
SEPARATION OF SOLVATED FIXED NITROGEN
FROM COMPOUNDS CONTAINING SAME
Filed May 29, 1958
3,044,853
2 Sheets-Sheet 2
47
=
'
WATER
4s
5
.h
50
u
MAKE-UP
1
SOLVENT
HYDROCARBON
DILUENT
5
AMMONIA
5:
5
ALKALI METAL HYDROX|DE—-L>‘
AMMONIUM HYDROXIDE
;
44/
g
I
—_
10
_
GAS FEED
I
"'
I
;
I.
42
"'"
AQUEOUASNIBJI/TSJQC ACID
AQUEOUS NITRATE
9
‘SUPPLEMENTAL
AIR
*1
FIG. 2
‘i
LUCIEN G. MAURY
GEORGE F. NAHILL’.
INVENTORS
BY
8M1;
AGENT.
3,044,853
United States Patent O?ice
Patented July 17, 19s:
O
‘I
a mixture of mono- and di-lauryl acid phosphates; triaryl
phosphates, e.g., triphenyl phosphate, tricresyl phosphate;
3,044,853
SEPARATION OF SOLVATED FIXED NITROGEN
FROM C(BMPUUNDS CONTAINING ‘SAME
diaryl, monoaryl and mixed mono- and diaryl phosphates,
e.g., mixtures of mono- and di-phenyl acid phosphates;
Lucien G. Maury, Newark, and George F. Nahill, Wil
mington, Del., assignors to Hercules Powder Company,
Wilmington, DeL, a corporation of Delaware
nitn'les, e.g., benzonitrile, stearyl nitrile, adiponitrile,
amides, e.g., dimethylformamide, dirnethylbenzamide,
methyl nonarnide; ethersppreferablyrcyclic ethers and
‘
Filed May 29, 1958, Ser. No. 738,813
14 Claims. (Cl. 23-157)
ethers containing more thanone'ether linkage, e.g., di
oxane, tetrahydrofuran, triethyleneglycol dimethyl ether,
This invention relates to the separation of nitrogen 10 ethylene ‘glycol dimethyl ether, and Carbowax'(trade .
name for a number of polyethylene glycol ethers’ of
oxides and/ or nitrous acid, as ?xedrnitrogen, from elec
tron donors containing same, by oxidation of the nitrogen
various molecular weights); sulfoxides, e.g., dimethylsul-f- '
compounds to nitric acid and recovery of the resulting
oxide and diethylsulfoxide; certain acetals, e.g., dimethyl
acetals; compounds containing two or more of the func
nitric acid as aqueous acid or a salt thereof. In one
aspect, this invention relates to the separation of ni 15 tional groups mentioned above such as hexamethyl phos
phoramide, ethyl ether of Z-hydroxyacetonitrile;organic
trogen oxides and nitrous acid, ‘from ?uids containing
same, by absorption in an electron donor material, and
acids, e.g., acetic acid; esters of organic acids, e.g., ethyl.
to the removal of the absorbed ?xed nitrogen from the
acetate; and certain ketones and aldehydes.
Thevfunction of the water so far as the improvement
resulting enriched donor material. In another aspect,
of the adb'sorption e?iciency of the donor compound is
this invention relates to a process for the absorption of
nitrogen oxides and/ or nitrous acid from gases contain
concerned appears to involve reaction of the solvated
ing same, in an electron donor solvent, and for the sub
ions to form solvated nitrous and/orsolvated nitric acid,
thereby emov'ing'the position of the equilibrium between
stantially simultaneous oxidation of the absorbed ?xed ni
the nitrogen oxides and‘ the solvated species away from
trogen to nitric acid, followed by removal of the resulting
nitric acid from the system by extraction either in form 25 the oxides, the result being concomitantly ‘lower vapor
pressure of the nitrogen oxide. Although the optimum
water concentration depends upon several factors, the
of the free acid or a salt thereof. In still another aspect,
this invention relates to the separation of nitrogen oxides
donor will generally contain from 2 to‘ 25 weight per
and nitrous acid from an electron donor containing same
by oxidation to convert the nitrogen compounds to nitric
acid followed by water extraction of the nitric acid as 30
Donor solvent miscible-water immiscible diluent ma
aqueous nitric acid. ‘In still another ‘aspect, this inven
terials are used in the solvent for the purpose of eifecting
tion relates to the separation'of nitrogen oxides and/ or
control of water concentration therein, there being a lini
nitrous acid from an electron donor containing same by
ited water concentration range for effecting maximum ab~
oxidation to convert the nitrogen compounds to nitric
sorption efficiency. a When employing a diluent, it is
acid followed by reaction of the nitric acid therein with 35 preferred that the donor solvent be one which is partially
miscible with water and to regulate the vwater concen~
ammonia or aqueous alkali metal (including ammonium)
hydroxide and removal of the resulting nitrate as aque
tration 'in the solvent by the presence of an amount of
diluent to provide the desired water concentration at
ous nitrate in high concentration.
In our copending application Serial No. 738,717, ?led
saturation so that a water saturated solvent can be,
May 29, 1958, is disclosed and claimed a process for
utilized. Thev degree of dilution, base upon the volume
cent
water.
’
V
.
.
’
ratio of donor solvent to diluent is ‘generally within the
‘range of from 0.2:1 topSzl, although values outside that
the utilization of certain electron donor compounds ‘as
selective absorbents for nitrogen oxides and nitrous acid,
the said electron donor compounds being chemically re
active. with the nitrogen oxides and/or nitrous acid only
range can be employed depending upon the solvent utilized
and the composition of ‘the ‘gas treated. Exemplary dilu
by sharing electrons therewith, and also exhibiting selec
ent materials are hydrocarbo'n'liquids such as kerosene, ,
tive solvent ‘action for acetylene. A still more e?‘icient
gas oils,’ saturated fuel oils, aromatic-hydrocarbons and
absorption of. nitrogen oxides and/or nitrous acid is
achieved in the practice of the process of the said co
pending application when water is present in the donor
troaromatics, aromatic ethers and various donor solvents '
the like, and halogenated aromatics and aliphatics, ni
themselves.
compound in controlled proportions.
When referring to electron donor compounds herein,
and in the above referred to copending application, it is
Electron donor compounds‘ particularly preferred'in , i
.the practice of the invention of the ‘above referred to‘ ' '
'copending application, are dimethylformamide, triethy-lé
eneglycol dimethyl ether, vvdirn'ethylsulfoxide, hexamethyl“
meant compounds that possess at least one unshared pair
of electrons which can become attached to a molecule
capable of accepting an electron pair. Many electron
donor-acceptor pairs are known, the donor-lacceptorcom
bination being referred to either as a complex or a solva
tion., The latter term is generally that applicable to those
bonds which are “weak” or “loose” and can be broken,
‘
~
55
phosphoramide, and tri-‘n-butyl‘ phosphate,’ ‘in view‘ of ~
the ‘ease with ‘which/Water content therein can ‘be regu
lated by the presence~ of a diluent.
‘ '
.
/
Although liquid'electron donor compounds are more ’
generally utilized in carrying out the process of the‘ above
referred to copending application, solid donor compounds j
employing conventional means, for recovery of ?xed ni
trogen from the enriched solvent.
can also be employed. By way of illustration, a slurry of
Electron donor solvents suitable for sharing electrons
with acetylene to form ‘a resulting bond with acetylene,
'pass200 mesh is suspended in an aqueous solution by‘ a
‘gas' stream ?owing through the suspension and containing‘ ,
such a. solid donor, e.g., triphenyl'rphosphate,'ground‘ to
as above described, are set forth in General Papers Pre
‘the ?xed nitrogen to be absorbed, under which conditions ‘
sented Before the Division of Petroleum Chemistry of
the American Chemical Society, No. 31, March 29 to
be utilized as a ?xed bedby absorption of water 'on the ;
April 1, 1954, Kansas City, Missouri.
solid absorbent and then passing the‘ nitrogen oxide‘.
the absorption takes place. The solid donor can also
Exemplary of electron donor compounds described
and/or nitrous ‘acid-containing gas stream through the"
bed. The same equilibria apply whether-the electron
herein are: trialkyl phosphates, e.g., tributyl phosphate,
triethylphosphate, and tri-2-etliylhexyl phosphate; di'alkyl I 70 ‘donor is solid or liquid;
'
,
'
~
~ - .
eElectron donor solvents are advantageously employed’, n
acid phosphates, e.g., diethyl acid phosphate vand dilauryl l
acid phosphate; mixed dialkyl, monoalkyl phosphates, e.g.,, in accordance with the process of the above said lcopende , 1
73,044,853
3
4
tion rate is sufficiently high at temperatures in the order
of 20—30° C. that higher temperatures, although they can
be employed, are generally not required. However, in
any event, the maximum temperature is limited by the sta
bility of the particular electron donor solvent employed.
Illustrative of top upper temperature levels employed
ing application in the separation of nitrogen oxides from
gases such as effluent gases from ammonia oxidation and
nitrogen ?xation, which usually contain from 2 to about
10 volume percent nitrogen oxides. However, the donor
solvents are advantageously applied to the scrubbing of
residual nitrogen oxides from waste gas streams contain
in carrying out the oxidation are those of certain solvents
set forth in the following tabulation.
ing same in low concentration, for example, a by-product
stream from the nitration of cellulose and containing
from about 0.1 to 0.3 volume percent or more of nitrogen
oxides. The said solvents can, however, be utilized for l0
other purposes such as a medium for reactions involving
liberation of nitrogen oxides wherein the said solvent re~
tains the liberated oxides to facilitate certain equilibrium
conditions, which oxide must then be removed from the
Upper
Temper-
Electron Donor Solvent
l. Trien-butylphosphate _____________________ __
solvent prior to reuse of same. Exemplary of such proc 15 2.3. Triphenylphosphate"
Dimethylformamiden
4. Dimethylsulfoxide ______________ ._
ess reactions are the nitration of aromatic or aliphatic
5.
Triethylene glycol dimethyl other
compounds, nitric acid oxidation of aromatic or aliphatic
6. Dioxane ________________________ __
compounds the nitrosation or diazotization of organic
amines, amides or imides and the processing of certain
ores and metals.
7. Diethylcne glycol dimethyl ether...
150
100
200
100
150
80
(10
50
160
100
70
40
___
150
100
8. Trlcresylphosphate _______________________ --
150
100
20
Although conventional distillation steps including vac
The oxidation rate is dependent upon certain variables,
and, in the case of nitrous acid in tri-n-butyl phosphate
donor, appears to ?t the following expression:
uum distillation and distillation at elevated temperatures,
extraction with aqueous base, and the like, can be em
ployed in the removal of the oxides and/ or nitrous acid
from the enriched donor compound, these methods in
volve high time and equipment requirements and are ‘ac
Preferred
Upper
ature
Limit, ° C.
Limit, ° C‘.
25
cordingly disadvantageously applied and particularly so
wherein t is in minutes, [N+3] represents molar concen
to continuous type operation. Further, in such continu
tration of the nitrogen compound, and [A] represents the
ous operation, the donor solvent to be recycled to the ab
effective concentration of the Lewis acid (moles per liter).
sorption system contains, unnecessarily, up to several per 30 In any event, the rate of oxidation increases with de
cent of residual absorbed ?xed nitrogen in view of the
creased concentration of water and/ or electron donor sol
limited time available for effecting substantially complete
vent and with increased concentration of nitrogen oxides
separation of those absorbed materials therefrom.
and nitrous acid and also with increasing concentration
This invention is concerned with a method utilizing
of Lewis acid.
an oxidation step for the removal of nitrogen oxides and 35 Extremely weak Lewis acid catalysts are much less
nitrous acid from electron donor materials containing
suitable in the practice of the invention. Accordingly we
same and provides a highly e?icient separation which is
prefer an acid catalyst having a Hammett Ho function of
particularly adaptable to continuous ?ow operation.
less than about +3.
An object of the invention is to provide a process for
The concentration of solvent and water contained
the removal of nitrogen oxides and/or nitrous ‘acid from
therein is conveniently regulated by the addition to the sol
electron donor materials containing same. Another
vent of controlled amounts of any solvent miscible-water
object is to provide a continuous ?ow type method for
immiscible liquid diluent employed in the process of the
the removal of nitrogen oxides and/ or nitrous acid from
above-referred to application, liquid hydrocarbons being
electron donor solvents containing same, by a combina
preferred, e.g., kerosene. Thus, the concentration of
tion of oxidation and nitric acid extraction steps. An 45 both donor solvent and water is varied in accordance
other object is to provide for the formation of ammonium
with the amount of diluent added, the greater the amount
nitrate from nitric acid in an electron donor solvent by re
of diluent the less the concentration of ‘water and solvent.
action with ‘ammonia followed by extraction of the re
Dilution of the solvent phase, therefore, contributes di
sulting ammonium nitrate salt. Another object is to pro
rectly to an increase in oxidation rate, i.e., in proportion
vide a method for the recovery of ?xed nitrogen from en 50 to the amount of diluent added. Generally a volume ratio
riched electron donor solvents previously employed as se
of donor solvent to diluent within the range of about
lective solvent in the absorption of nitrogen oxides and/or
0.1:1 to 10:1 is advantageously employed.
nitrous acid from a ?uid containing same. Another
The amount of Water present in the solvent phase is
object is to provide a method for the manufacture of
preferably in excess of that required for the oxidation re
nitric acid and salts thereof from a stream containing ni 55 action and is generally present in a volume ratio of donor
trogen oxides and/or nitrous acid by simultaneously ab
solvent to Water within the range of about 0.11 :1 to 10:1,
sorbing the oxide and/ or nitrous acid and oxidizing same
preferably about 0.4:1 to 3:1.
In the utilization of free oxygen as the oxiding agent,
to nitric acid for extraction as aqueous nitric acid or a salt
thereof. Other objects and aspects Will be apparent in
light of the accompanying disclosure and the appended
claims.
In accordance with the invention, an electron donor
compound is separated from nitrogen compounds of the
any suitable gas stream can be employed so long as the
nonoxygen components thereof are chemically inert in
the system. Thus, air, diluted with nitrogen or carbon
dioxide, or the like, can be advantageously employed.
Generally, the nitrogen oxide-containing stream is one
group of nitrogen oxides and nitrous acid contained there
obtained from a process utilizing air, such as an ammonia
in in solvated form by contacting the said donor com~ 65 oxidation or a nitrogen ?xation process so ‘that the resi
pound with an oxidizing agent in the presence of a Lewis
dual free oxygen functions as the oxidizing agent with
acid under conditions for converting said nitrogen com
out the need for adding a supplementary oxidizing stream.
pounds to nitric acid, and when a nitrogen oxide is pres—
Although we prefer generally to employ a gaseous
ent, maintaining a sn?icient amount of water in the zone
stream of oxiding agent, as described above, numerous
of said contacting to react withthe said oxide to form 70 other oxidizing agents can be utilized if desired. Thus,
nitric acid, and then removing nitric. acid, so produced,
from the said compound.
The oxidation step can be carried out at any tempera
ture suitable for oxidizing nitrous acid to nitric acid
hydrogen peroxide, perchloric acid, potassium, perman
ganate, potassium dichromate, perchloric acid or its salts,
peroxides such as peracetic acid, sodium peroxide, cumyl
peroxide and the like can be employed. These oxidants
utilizing free oxygen as the oxidizing agent. The oxida 75 can ‘be used in conjunction with air, if desired. Thus,
3,044,853
5
by way of further example, the rate of air oxidation of
nitrogen oxides and nitrous acid in chamber 26 to nitric
nitrogen trioxide is greatly increased by adding hydrogen
acid.
'
The liquid-gas temperature in chamber 26 is generally
peroxide to the solution.
in the order of 20—30° C. but in any event below thermal
reference
The above
to t-ri-n-buty-l
form of phosphate
kinetic expression
varies somewhat
set forth from
instability temperatures of the solvent. Air introduced
into chamber26 is added in proportions to provide free
solvent to solvent but in any event the effect of dilution as
above described is the same. In some cases, such as in
oxygen in an amount generally in excess of the stoichi
the case of dimethyl form-amide, the reaction rate is pro
ometric proportions of nitrogen oxides and nitrous acid
portional to the ‘oxygen pressure, whereas in the case of
to be oxidized to nitric acid. Total liquid from cham~
tri-n-butyl phosphate oxygen pressure does not affect the 10 ber 26, containing nitric acid, is discharged via line 31
to any suitable liquid treating zone 3'2 wherein residual
oxidation rate.
gas is ‘separated for discharge via line 33 and wherein
The invention is illustrated with reference to ‘FIG
total liquid phase from line 31 is treated vfor removal
URES 1 vand 2 of the drawings, each of which illustrates
an embodiment wherein the electron donor solvent en
of nitric acid as aqueous nitric acid ‘and/or aqueous am
riched by absorption of nitrogen oxides and/or nitrous
acid, from gas streams containing same, is separated from
monium nitrate via line 34 to'provide residual solvent
for recycle via lines 35 and 12 to chamber 11.
Electron donor containing nitrogen oxides land/or
its absorbed ?xed nitrogen components by ‘oxidation of i
the same to nitric acid followed by removal of the result
ing nitric acid from the system.
nitrous acid can be introduced via line 29 into cham
ber 26 from any source together with or in "lieu of that
passed to chamber 26 from chamber 11 and line 23 as
4
With reference to FIGURE 1, an e?luent nitrogen
oxide-containing gas stream such as from ammonia oxida
tion, or nitrogen ?xation, or the like, and containing from
0.2 to 11 volume percent nitrogen oxides is passed into
desired, water being added, when desired, vialine 22a.
Particularly in the practice of that embodiment, lean
donor solvent from zone 32 can be withdrawn via line
chamber 111 via line 10 in countercurrent ?ow contact
40 in lieu of recycle to an absorption zone 11. -
with downwardly ?owing electron donor solvent such as. 25
tri—n-butyl phosphate introduced from line .12 via dis
, ‘
We have found that the distribution coe?icient for
nitrous acid, i.e.,v ratio of HNO2 rnolarity in water to
HNO2 molarity in the donor solvent is in the order of
tributor member 13 and passed over the surfaces of a suit
able packing 14 such as Raschig rings, or saddles, or the
about 0.002 to 0.05 depending upon temperature,- con
centrations and pH of the solutions.
like supported on perforate support 9'.
The donor solvent in contact with packing 14 in cham
ber 11 contains water in the above described molar ratio
Oonsequentlyk
separation of nitrous acid from the donor solvent by >
water washing is unsatisfactory. Separation of nitrogen
oxides from the donor solvent is ‘also unsatisfactory in
range, preferably in a solvent to water molar ratio of from
about 0.421 to 3:1 and is diluted with a suitable hydro
carbon oil diluent such as kerosene in the above described
view of the low coe?‘icient of distribution of the oxides
from the solvent into the water. However, we have
35 found that the distribution coe?icient of nitric acid, be
volume ratio of donor solvent to kerosene.
tween the donor solvent and water is generally'in the
The absorption in chamber 11 is maintained at any
suitable temperature, the upper temperaturebeing limited
range of about 1:1 to 20:1, i.e., ratio of nitric acid ex
tracted into the water to nitric acid remaining in the
to that at which the solvent is thermally stable, which for
solvent. Accordingly, the oxidation in conjunction with
tri-n-butyl phosphate is as high as about 150° C. How
ever, a temperature of, say, 20-30" C. can be utilized in 40 subsequent water extraction, in accordance with the in
vention, is most [advantageously employed tov 'e?ect an
most instances. The diluent, e.g., kerosene, as above de
ei?cient removal of the nitrous acid and nitrogen oxides
scribed, serves as a regulant for water concentration in
from the solvent to provide for its recycle to the absorp
tion zone. One such step in zone 32 is, therefore, 'a
water extraction of nitric acid from the residual liquid
and discharge of resulting aqueous nitric acid via line 34.
the solvent during absorption. As disclosed and claimed
in the above referred to copending application, the donor
solvent absorption efliciency is greatly facilitated by the
presence of a limited amount of water, the ‘ optimum
amount being somewhat di?ferent for each solvent. How
We have further discovered that an even more e?i
ever, the volume ratio of donor solvent to diluent, em
cient removal of nitric acid from the solvent in zone
ployed for the absorption, is usually in the above de
32 is accomplished by passing ammonia gas or aqueous
alkali metal hydroxide, or ammonium hydroxidein con
scribed volume ratio range of from 0.2:1 to 5:1.
Residual gases are passed from chamber :11 via line 16
tact with the nitric acid-watencont-aining donor solution .
to scrubber 17 through a body of scrubbing liquid therein
to form. alkali metal or ammonium nitrate. Resulting,
nitrate formed by reaction with at least one of the am
such as a hydrocarbon oil which is of the same composi
tion as the diluent in chamber 11. Oil in chamber 17 en
monia alkali metal hydroxide and ammoniumhydroxide
traps any solvent vapors passed via line 16 and resulting 55 is passed from the system via line 34 ‘as aqueous nitrate.
The nitric acid salt route is particularly advantageous in
enriched oillis returned to chamber 11 via lines v,frtia and”
Residual gases are passed from chamber 17 via line~ ' view of the high distribution coe?‘icient for ammonium .
1812. Make up oil absorbent for‘charnber, ‘[17 is added‘ ' nitrate between the water phase and the solvent phase
via conduit 18c. Kerosene is a preferred solvent diluent
which is in the order of 50—500 times greater than that
for tri-n-butyl phosphate and is ‘generally utilized in a 60 for nitric acid as illustrated with reference to the fol; ,
21.
lowing tabulation:
volume ratio to tri-n-butyl phosphate, prefer-ably up to
about 3:1. Initially added oil, water, and donor solvent
as well as any required make up proportions of these
Species
liquids are introduced into the system respectively via
lines 20, 22 and 25.
a
Total liquid phase, including enriched solvent, water,
Distribution \
Water-
65
Organic Phase
Extracted
_
and diluent, is passed from chamber 11 into chamber 26
via line 23, pump 24 and line 27, together with air as
Tri-n-butyl Phosphate __________________ __
1.1
50731'%‘n=1r;butyl Phosphate, 50% Kerosene
2. 8
non
.
EN 03 _____ __ 20% Tii-n-butyl Phosphate, 80% Kerosene
an oxidizing gas introduced via line 28. v Total liquid and
EN 02 _____ __
'l‘ri-n-butyl Phosphate (no diluent) _____ __
oxidizing gas is passed upwardly through chamber 26 in 70 NH4NO3_-__ Tn-n-bntyl Phosphate (no diluent) _____ __
NH4NO3_.._ 50% 'I‘n-n-butyl, 50% Kerosene..."
contact with a solid Lewis catalyst 30 such as an ion ex
change resin, for example, a polymerized sulfonated vinyl.’v . '.
benzene (Dowex 50, Dowex SO-W, Amberlite-IR-IZO), a
Coe?icient 1
NaNOa ____ __ 20% Tl‘i-n-butyl, 80% Kerosene __________ __
7. 5
0.01
500 ‘
1000
100,
‘ ' 1 Ratio of molarity or acid or salt in water to molarity of acid or salt in
organic phase.
the like, which serves as a catalyst for the oxidation of 75 As noted with reference to the above tabulation, am
polyacrylic acid (Amberlite IRC-SO), a'zeolite clay, or
-
3,044,853
8
7
monium nitrate distribution coefficients are higher when
The nitric acid is extracted into the water layer 42,
the donor solvent contains a diluent oil than when no
diluent is present. Accordingly, when a diluent is
present in the solvent, somewhat higher aqueous nitric
acid concentrations in the water phase can be accom
which extraction is facilitated by flow of make up water
from line 47 to column 4-2 via the solvent body 43. A
dilute aqueous solution of nitric acid is withdrawn from
the water column 22 via line 28’. By adjusting the rate
plished than when no diluent is present. As further
illustrated with reference to the table, by passing am
monia through the solution, or by extraction with
aqueous sodium hydroxide or ammonium hydroxide,
after oxidation, the distribution coe?icient of the nitrate
is many times greater than that of the nitric acid, ob
tained when utilizing straight water extraction.
of water addition, the concentration of nitric acid formed
can be controlled to provide acid concentrations of from
10 to 40 percent or higher. Additional agitation is pro
vided by the ?ow of air fed through the water layer as
With reference to FIGURE 2 is illustrated ‘an embodi
ment wherein nitrogen oxides and nitrous acid are ‘ab
sorbed from a gas stream containing same and simul
or nitrous ‘acid or those absorbed from the feed into the
water, back into the solvent so that very little, if any,
nitrogen oxide or nitrous acid is lost to the aqueous
stream withdrawn via line 28'.
part of the gas feed stream, or as a supplementary
stream, to facilitate extraction of nitric acid into the
water layer and to blow unoxidized nitrogen oxides and/
taneously oxidized, to provide nitric acid for removal
Free ammonia, or aqueous alkali metal (including
ammonium) hydroxide, can be introduced into the cham
ber 41 via line 51 in contact with solvent 43 to react with
acted in situ with ammonia, ammonium hydroxide or
alkali metal hydroxide to form the corresponding nitrate, 20 nitric acid therein to form alkali metal (or ammonium)
nitrate in situ. Alkali metal, or ammonium, nitrate is
which is characterized by a distribution coefficient
extracted into water in chamber 41 and withdrawn from
markedly higher than that of nitric acid, above described.
water column 42 as aqueous nitrate via line 28'. Alkali
Nitrous acid 1and/ or nitrogen oxide-‘bearing feed gas is
metal hydroxides introduced into the system via line 51
introduced via ‘line 10' into chamber 41. Gas fed
are less satisfactory than ammonia or ammonium hydrox
through line 10’ is generally that from a process con
ide as is apparent from the distribution coe?icient there
taining air so that a su?‘icient amount of free oxygen
for shown with reference to the table hereinabove.
is present for accomplishing oxidation of the nitrogen
The following examples are further illustrative of the
oxide and/or nitrous acid components to nitric acid.
invention.
Feed gas from line 10' is passed into chamber 41 up
EXAMPLE 1
wardly through water column 42 and electron donor 30
from the system in aqueous form or as aqueous nitrate
via line 28’. When desired, the nitric acid can be re
solvent 43, preferably tri-n-butyl phosphate. Solvent ‘43,
A series of groups of runs was made employing appara
water saturated and containing a hydrocarbon diluent
from line 50, preferably kerosene, in a volume ratio of
donor solvent to diluent of from 0.2:1 to 5:1, is super
posed on water column 42 at interface 44, and is in con
tus constituting separate absorption and oxidation cham
bers of the type illustrated with reference to FIG. 1 cm
ploying in all instances tributyl phosphate (TBP) as the
electron donor solvent together with a kerosene fraction
tact with solid Lewis acid 46 within the solvent body 43.
Nitrous acid and/ or nitrogen oxide-containing gas passes
upwardly through the water column 42 without apprecia
ble reaction with the water. The nitrogen oxides and/or
as the hydrocarbon oil diluent.
Each series of runs was
made at a temperature, in each chamber, of about 25° C.
and at the pressure designated. The procedure was that
nitrous acid are then simultaneously absorbed in solvent 40 consonant with description hereinabove with reference to
process of FIG. 1. The resulting data are set forth in the
43 and air oxidized in contact with catalyst 46 to nitric
following tabulation (Table I) with reference to like
acid at under temperature conditions the same as that
numbered streams of FIG. 1.
described with reference to chamber 26 of FIGURE 1.
Table l
Grams per Hour
Group I X
N2
0:
1120 N02
NO TBP
Oil
IINO; HNO: NHQIO;
Line No. of
F12. 1:
1O ____ __
3, 570
1, 080
50. 5
7. 3
4.8 ____________________________________ __
12+21__ ________________________________ __
598
548
11.5
0
f)
23 ______________________________________ ._
598
548
13.5
10. 0
I)
31 _ _ _ _ _ _
__ _ _ _ _
_ . . _ __
34 ______________________________________ __
l6 ____ __
3, 570
1,080
50. 5
0
1. 9
598
548
26.1
0. G
598
548
11.5
0. (3
0
19. 6
____________________________________ ..
Grams per Hour
Group II '-’
N2
02
1120 NO
NO 'I‘BP
Oil
HNO; l'lNO: NIIlNOg
3,044,853
Grams per Hour
Group III 3
.
N2
0;
E20. NO;
3, 430
1,040
NO TBP
Oil
HNO3 HNOz NH4NO3
Line No. of
lg. 1:
10 ____ __
12+21__
505
____ __
14. 6
9. 5 __________________________________ --__..
786
720
15
0
23
31
________________ __
____ _ _
786
.786
720
720
17
50
34
. ___ _ _
786
720
15
16 ____ __
3, 430
1, 040
_ _ _ _ __
505
0
_
.4
.8
0
O
. 8
44. 4
1 9
Grams per Hour
Group IV 4
N2
03
E20 N02
4,270
1, 510
NO TBP
Oil
HNOa HNO: NH4NO3
Lme N o. of
Fig. 1:
10 ____ __
7.2
14 6
9 5 ____________________________________ __
12+21__
23 ____ __
31
____ _ _
. _ _ _ __
34
16 ____ __
1 0.20
9 1.25
3 0.40
4 0.40
4, 270
volume
volume
volume
volume
1, 510
7. 2
0
720
660
14.0
"
720
660
16.0
.4
720
660
49. 2
.7
720
660
14. 0
.7
1 9
0
0
0
44. 8'
--
percent nitrogen oxides in gas stream 1.0 atmos.
percent nitrogen oxides in gas stream 1.0 atmos.
percent nitrogen oxides in gas stream 1.0 atmos.
percent nitrogen oxides in gas stream 6.0 atmos.
.
pressure.
pressure.
pressure.
pressure.
EXAMPLE 2
, The following kinetic expression also referred to here
The ‘following tabulation, Table II, sets forth run data
which demonstate the oxidation reaction of the process of
this invention. In each run, the solution of nitrous acid
inabove, was found to characterize the rate of nitrous
in the donornsolvent was ‘prepared so as to contain ?xed
nitrogen having an average oxidation state of 3. The
k =Rate [H2O][TBP]
acid oxidation (Table II) in the tribntyl phosphate donor
solvent:
I
1
[HNOzrliA]
‘resulting solution was transferred to a Parr shaker cham
wherein all quantities are expressed as vgram mols'per
liter and “TBP” land “A” designate tributyl phosphate and
ber, mounted on a shaker. The gas reservoir of the Parr.
‘shaker was ?ushed With nitrogen and oxygen was then
acid respectively. Although the foregoing kinetic‘ ex~
introduced into the closed chamber, together with opera
tion of the shaker to provide agitation. Oxygen was fed
‘into the reaction mixture "at a rate su?icient to maintain
pression is not ‘followed exactly when donor solvents
other than tributyl phosphate ‘are utilized, the value of
jconstant pressure shown in Table II. From the rate of
feed of oxygen the'total amount of nitrous acid oxidized
rate in each instance.‘
was determined.
, 'Asindicated by ‘the k1v values of’ Table II the total
k1, although approximate, is indicative of'the reaction
corroborative tests for determination "
of the degree of nitrous acid oxidation were made by
analysis of the ?nal product for nitrous and nitric ‘acid.
The nitrous acid was found to have been stoichiometrical
1y converted to nitric acid.
,
.
'
,
I
v
Table
‘
acid concentration in the reaction mixture, i.e., including
the‘ acid’ catalyst and nitric acid present, increasesthe re»
actionratein proportion to the amount of acid present.
' This demonstrates‘ in light of the ‘above kinetic expres
II
_
OXIDATION OF NITROUS ACID, IN TRIBUTYL PHOSPHATE, TO NITRIC ACID
M1.
Run N0.
M1. Solvent
,
Ml.
‘
Cyclo-
‘
[HNozlus'
Grams Lewis Acid
° 0.
P02,
Catalyst
Temp.
p.s.i.
Water hexane
[HNOz??s
k1
Gram moles/liter
50
50
50
50
0
0,
0
75
50
75
3
0
50
0
26 ,
21 ‘
23
22
_
oWex-50-W 7__
do. 7.
3. 5
8. 0
8. 0
8. 0
2. 00
2. 00
2. 00,
2. 00
.
0. 73
.37
. 00
. 37
2. 00
. 73
0.20
0.18
0.20
0. 20
27
8. 0
25
8. 0
2. 00
. 37 .
. 21
23
1. 5
2.00
.37
. 20
. 18
20
0
25
8. 0
1. 50
. 28
~. 011
20
20
20
50
0
0
0
0
8. 0
8. 0
8. 0
3. 5
1. 50
1. 50
1;’ 50
2. 00
. 28
. 28
. 28
.73
~.06
~. 1
~. 045
5 ~. 2
50
0
20 Silica-alumina
2.0 NaOH.--
23
23
23
25
27
8.0
2. 00
50
0
20 Super ?ltr
26
3. 5
2. 00
. 73
° ~. 2
50
_
1 Tributyl phosphate.
1 Dimethyl formamide.
3 Dimethyl sulfoxide.
4 Triethylene glycol dimethyl ether.
15 Rate constant was calculated based on silica-alumina catalyst acidity of 2.0 mequiv. per gram.
6 Rate constant was calculated based on Super ?ltrol catalyst acidity of 0.35.1nequiv. per gram.
7 A polymerized sulfonated vinyl benzene.
8 Initial concentration.
0
.
0.00
-.
3,044,853
12
11
molar solution of nitric acid. The pressure of the system
sion that the total acid ‘functions as a catalyst for the
oxidation, and in no other manner, which is further il
was a ‘few mm. above atmospheric.
lustrated with reference to run No. 13 wherein no reac
marized in the following tabulation.
tion was obtained when the solution was basic rather
than acidic.
EXAMPLE 3
The data are sum
Table V
A stream of air containing, on a weight basis, 0.14
percent NO and 0.30 percent N02 was passed into and
through apparatus, of the type illustrated with reference
Outlet Gas
Aqueous Etiluent
Time From
Composition,
Composition, Molarity
Start of
Run
Wt. Percent
to FIG.‘ 2 of the drawings, containing a layer of 150 ml.
(Min)
superposed on a layer of 100 ml. of water, in the presence
of about 0.2 molar nitric acid as the catalyst. Effluent
gas from the chamber was analyzed periodically by pass
0. 04
0.07
0. 08
ing the same through a condenser and a 100 mm. spec
0.07
0. 07
trophotometer absorption cell, the gas being thereby con
tinuously analyzed by the ultraviolet absorptivity at
cent
Nitrogen
Oxides
ltccovcrcd
NO
of tri-n-butyl phosphate ‘as the liquid donor solvent
Wt. Per
N01
0.02
0.02
0.02
0.02
0.03
HNOZ+IINO3
>0. 20
0. 25
0. 30
0.35
0. 39
IINO:
<0. 002
<0. 002
<0. 002
<0. 002
<0. 002
as Nitric
Acid
87
80
78
80
78
2260° A. for NO and 4480“ A. for NO2+N2O4. Water
was continuously introduced at the top of the chamber 20
The invention, although generally applied to the sep
above the donor solvent layer at a rate of 60 mL/hour,
aration of ?xed nitrogen from liquid electron donor com
the gas stream being fed at a rate of 3000 cc./minute.
pounds, is nevertheless applicable to separation of ?xed
The system was maintained at room temperature and at
nitrogen from solid donor compounds. Thus, a solid
atmospheric pressure, at a constant liquid level. The fol
lowing tabulation, Table III, sets forth the outlet gas and 25 donor, e.g., ground triphenyl phosphate, enriched with
absorbed nitrogen oxides and/or nitrous acid is slurried
aqueous e?luent composition.
, with water and a body of Lewis acid, preferably liquid,
to e?ec-t the oxidation step. In this manner, the nitric
acid formed is extracted into the Water phase for re
Table III
30 covery as aqueous nitric acid, and residual solid donor,
substantially free from absorbed ?xed nitrogen, is in con
Tlme From
Start of
Outlet Gas
Aqueous Effluent
Wt. Per
Composition,
Wt. Percent
Composition, Molarity
cent
Nitrogen
Run
dition ‘for reuse.
As particularly illustrated with reference to the draw
ings, the enriched liquid electron donor solvents to which
the oxidation step of the invention is preferably applied
are those of the now preferred group herein referred to
with reference to copending application Serial No. 738,
Oxides
(Min)
Recovered
NO
0. 08
0.08
0. 10
0. 10
NO:
HNOz+HNO3
0.00
0.01
0.01
0.01
>0. 20
>0. 20
0. 35
0. 40
HNO:
<0. 002
<0. 002
<0. 002
<0. 002
as Nitric
Acid
82
82
78
78
717, namely, dimethylformamide, triethyleneglycol di
methyl ether, dimethylsnlfoxide, hexamethyl phosphor
4.0 amide, and tri-n-butyl phosphate. These solvents, upon
being freed from ?xed nitrogen, are easily separated from
water phase in contact therewith, for reuse, or when de
sired can be easily maintained water saturated, at a de
EXAMPLE 4
sired water concentration value, by the presence of
diluent therein. These solvents, therefore, are particular
ly adaptable to the regulation of oxidation rate, and of
the distribution coe?icient of nitric acid and/ or the nitric
A run similar to that of Example 3 employing the
same apparatus was carried out except that the donor
solvent consisted of 85 ml. tri-n-butyl phosphate and 85
acid salt between the solvent and water.
ml. decalin. The water layer consisted of 55 ml. water
However, when substantially completely water miscible
and contained, as an acid catalyst, 45 grams of a sul
solvents are employed, water content in the solvent can be
fonated polymerized vinyl benzene, an ion exchange resin 50 regulated by use of a diluent, although generally a larger
containing 4 milliequivalents H+ gram. The data are
amount of diluent is required than for partially water
summarized in the following tabulation.
miscible water solvents. Nitric acid or nitric acid salts
are, in the case of removal of ?xed nitrogen from highly
55 water miscible solvents, separated by distillation of the
Table IV
Time From
Outlet Gas
Composition,
Start of
Run
Wt. Percent
(Min.)
252 __________ __
1,275 ________ -_
1,381 ________ __
1,424 ________ -1,509 ________ _.
NO
0. 07
0.09
0.08
0.07
0. 08
NO:
0. 03
0. 03
0. 04
0. 04
0. 05
Aqueous E?luout
Composition, Molarity
HNOrl-HNOg
O. 30
0.39
0.26
0. 20
0. 18
HNO:
nil
nil
nil
Ilil
nil
Wt. Per
cent
Nitrogen
Oxides
total liquid body of solvent and diluent and Water dis
placed from the solvent by the diluent, or alternatively, by
distillation of the two separate phases.
By the term Lewis acid, it is meant “a substance capable
60 of accepting a pair of electrons from a base” (G. N. Lewis,
Recovered
“Valence and the Structure of Atoms and Molecules,”
as Nitric
Acid
78
73
73
75
7].
the Chem. Cat. Co., N.Y.C., 1923). Exemplary of various
Lewis acids are Bronstead acids (e.g., nitric, sulfuric, hy
drochloric, phosphoric, acetic, benzoic acids), acid clays,
65
(e.g., silica alumina, super?ltrol, cracking catalysts), ferric
chloride, aluminum chloride and the like.
When referring herein to the removal of nitrogen oxides
from donor compounds we are aware that electron donor
compounds contemplated herein generally exhibit rela
70 tively little, if any, absorptive power for nitrous oxide
and pure nitric oxide. Therefore, although it is Within the
EXAMPLE 5
scope of the invention to separate the donor solvent from
A run similar to that of Example 4 was made except
all nitrogen oxides contained therein, nitrous oxide and
pure nitric oxide, if present in the solvent phase to be
that the water layer contained 75 ml. water, the water
rate was 250 ml./hour, and the acid catalyst was a 0.2 75 oxidized, will be present in a very small proportion.
3,044,853
13
14
As will be evident to those skilled in the art, various
modi?cations can be made or followed, in the light of the
absorbed nitrogen compound from said electron donor
compound, the said process comprising passing the said
foregoing disclosure and discussion, without departing
gas together with a free oxygen-containing gas upwardly
through a layer of water and then through a layer of said
scope of the claims.
5 electron donor compound superposed on said water layer
What we claim and desire to protect by Letters Patent is:
and containing a layer of solid acid material characterized
1. In a process. for the separation of an electron donor
by a Hammett Ho function less than +3 under conditions‘
compound from a nitrogen compound solvated therewith
for carrying water in said gas from said water layer into
from the spirit or scope of the disclosure or from the
said liquid donor compound layer to provide a mole
and selected from the group consisting of nitric oxide,
nitrogen dioxide, nitrogen trioxide, nitrogen tetroxide, 1O ratio of said donor to Water contained therein within the
nitrogen pentoxide and nitrous acid, said electron donor
compound being chemically reactive with said nitrogen
compound only by sharing electrons therewith and also
range of from 0.4:1 to 10:1 and for causing solvation of
said nitrogen compound with said electron donor com
pound and oxidation of the resulting solvated ‘nitrogen
compound, by said free oxygen-containing gas, to nitric
sharing electrons with said acetylene, and said donor com 15 acid, and when the said nitrogen compound-containing gas
pound being selected from the group consisting of glycol
contains nitric oxide, maintaining the average oxidation
exhibiting selective absorption action for acetylene by
ethers, alkyl phosphates, aryl phosphates, dialkyl amides,
alkyl sulfoxides and alkyl phosphoramides, the improve
state of the total ?xed nitrogen therein at a minimum of
3.0, the said electron donor being reactive with said
ment which comprises contacting the electron donor com
nitrogen compound only by sharing electrons therewith
pound-nitrogen compound solvate with a free oxygen 20 and exhibiting selective solvent action for acetylene by
sharing electrons with said acetylene and being selected
, containing gas in the presence of an acid material charac
terized by a Hammett Ho function less than +3 under
\from the group consisting of glycol ethers, alkyl phos
temperature conditions for effecting oxidation of the said
phates, aryl phosphates, dialkyl amides, alkyl sulfoxides
solvated nitrogen compound by said free oxygen-con
and alkyl phosphoramides, passing residual gas from the
taining gas to nitric acid, and when said solvated nitrogen 25 zone containing said layers of water, acid material and
compound is a nitrogen ‘oxide, maintaining a su?‘icient
donor compound and extracting resulting nitric acid from
amount of water in the zone of said-contacting to react
said layer of electron donor compound into said water
the said oxide together with oxidation of same by said free
layer.
,
'
oxygen-containing gas to cause the said oxidation to nitric
8. A process for the removal of a nitrogen compound
acid, and then removing nitric acid so produced from the 30 selected from the group consisting of nitric oxide, nitrogen
resulting electron donor compound-nitric acid mixture.
2. A process of claim 1, wherein said donor compound
dioxide, nitrogen trioxide, nitrogen tetroxide, nitrogen
pentoxide and nitrous acid, from a gas containing same,
including the steps of absorbing said nitrogen compound
is a liquid.
in a liquid electron donor compound, described herein
, 3. A process of claim 2, wherein said donor compound
is incompletely miscible with water, and said nitric acid 35 after, and separation of the absorbed nitrogen compound
is removed from said donor-nitric acid mixture by water
from said electron donor compound, the said process
washing, as aqueous nitric acid.
comprising passing said gas through a ?rst zone in contact
4. A process of claim 2, wherein said donor compound
therein with said liquid electron donor compound in the
is incompletely miscible with Water, and said nitric acid
presence of water in an amount providing for a mole ratio
is removed from said donor compound nitric acid mixture 40 of said donor compound to water therein within the range
by contacting said mixture with a compound selected
of from 0.4:1 to 10:1 under conditions causing absorption
from the group consisting of free ammonia, ammonium
of said nitrogen compound by said electron donor, where~
hydroxide and an alkali metal hydroxide to react samev
by said nitrogen compound is solvated with said electron
with said nitric acid to form a nitrate, followed by water
donor, and when said gas contains nitric oxide, maintain
washing the resulting nitrate from said donor.
45 ing the average oxidation state of the total ?xed nitrogen
5. A process of claim 2, wherein a hydrocarbon diluent
therein at a minimum of 3.0, passing total liquid from said
is maintained dissolved in said donor to regulate the
‘ ?rst zone into a second zone, together with a free oxygen
content of water therein, wherein the volume ratio of
containing gas, in contact with a solid acid material char
said donor compound to said water is within the range of
acterized by a Hammett Ho function less than +3, in the
from 0.1 :l to 10:1, and wherein the volume ratio of said 50 presence of water, under conditions for effecting oxidation
liquid donor compound to said diluent is within the range
of from 0.2:1 to 5:1.
of the said solvated nitrogen compound by said free oxy
gen-containing gas to nitric acid, and removing said nitric
6. In a process for the separation of tri-n-butyl phos
phate from a nitrogen compound solvated therewith and
donor, said electron donor compound being reactive with
acid from the resulting mixture of same with said electron
selected from the group consisting of nitric oxide, nitrogen - 55 said nitrogen compound only by ‘sharing electrons there
dioxide, nitrogen trioxide, nitrogen tetroxide, nitrogen
with and exhibiting selective solvent action with acetylene
by sharing electrons with said acetylene and being selected
pentoxide and nitrous acid, and the resulting tri-n-butyl
phosphate-nitrogen compound solvate being a liquid, the
improvement which comprises passing a stream of said
from the group consisting of glycol ethers, alkyl phos
aryl phosphates, dialkyl amides, alkyl sulfoxides
tri-n-butyl phosphate containing said nitrogen compound 60 phates,
and alkyl phosphorarnides.
solvated therewith in contact with a free oxygen-containing
9. A process of claim 8 wherein said liquid
gas and a solid acid material characterized by a Hammett
donor is tri-n-butyl phosphate.
Ho function less than +3, in the presence of water, under
10. A process of claim 8 wherein said liquid
conditions suitable for effecting oxidation of the solvated
nitrogen compound by said free oxygen-containing gas to 65 donor is dimethyl formamide.
11. A process of claim 8 wherein said liquid
nitric acid, passing separate streams of residual gas and
donor is triethylene glycol dimethyl ether.
total liquid from the zone of the said contacting, and then
removing nitric acid from the said total liquid.
12. A process of claim 8 wherein said liquid
7. A process for the removal of a nitrogen compound
donor is dimethyl sulfoxide.
selected from the group consisting of nitric oxide, nitrogen 70 13. A process of claim 8 wherein said liquid
dioxide, nitrogen trioxide, nitrogen tetroxide, nitrogen
pentoxide and nitrous acid, from a gas containing same,
including the steps of absorbing said nitrogen compound
in an incompletely water-miscible liquid electron donor
compound, described hereinafter, and separation of the 75
electron
electron
electron
electron
electron
donor is hexamethyl phosphoramide.
,
14. A process of claim 7 wherein said liquid electron
donor is tri-n-butyl phosphate.
3
(References on following page)
3,044,853
15
16
References Cited in the ?le of this patent
FOREIGN PATENTS
UNITED STATES PATENTS
400,207
2,132,511
2,566,197
267,874
Germany ------------ —- NQV- 27, 1912
Hake ________________ __ Mar. 26, 1889
OTHER REFERENCES
Hentrich et a1 __________ __ Oct. 11, 1938 5
Webb: “Absorption of Nitrous Gases,” Longmans,
Hass et a1 ____ _.._ _______ __ Aug. 28, 1951
Green & C0,, New York, N.Y., 1923, page 120.
UNITED STATES PATENT OFFICE
CERTIFICATION OF CORRECTION
Patent No. ‘3,044,853
July 17, 1962
Lucien G. Maury et a1.
It is hereby certified that error appears in the above numbered pet
ent requiring correction and that the said Letters Patent should read as
corrected below.
Column 2, line 40, for "base" read —— based --; column 4,
in the tabulation, first column, last line thereof, for
"Trlcresylphosphate" read -- Tricresylphosphate —-; column 6,
in the tabulation, second column, and opposite “NH4N03", for
“50% Tri-n-butyl" read —- 50% Tri—n—butyl Phosphate —-; same
column, and opposite "NaNOg", for "20% Tri-n-butyl" read
'-- 20% Tri-n-butyl Phosphate ——; column 11, line 51, for "W
gram." read —- [LR/gram. -—.
Signed and sealed this. 6th day of November 1962.
(SEAL)
‘
Attest:
.
ERNEST w. SWIDER“
Attesting Officer
DAVID L. LADD
Commissioner of Patents